The present invention relates to a machine for automatically cutting sheet material. More precisely, the invention relates to a machine for cutting stacks or lay-ups of sheet material, in particular textile material, using a cutter head.
Such machines are themselves well known. Reference can be made for example to document EP 0 658 087 B1. They essentially comprise a bench having a cutting zone proper, a zone for loading sheet material for cutting at an upstream end of the cutting zone, and a zone for unloading cut parts from a downstream end of the cutting zone.
The loading zone is used for initially stacking a plurality of sheets, e.g. of textile material, so as to cut out parts simultaneously from the set of stacked sheets. Under the cutting zone, there is a cutter conveyor that is used for entraining the stack of sheets during the cutting operation. Cutting is performed using a cutter head that is mounted on means enabling it to move relative to the bench, and in particular on a gantry that itself moves along guides placed along the length of the cutting zone, the cutter head being capable of moving in translation along the gantry. Finally, the unloading zone serves to transfer the stack of sheets once they have been cut up.
Within the structure of the bench, the machine also comprises a suction device enabling a high degree of suction to be established in the cutter conveyor, possibly as much as 200 mbar. The suction device thus serves to hold the sheets for cutting stationary while they are being cut. To obtain effective suction, it is generally necessary to place a film of airtight material over the top of the stack of sheets for cutting.
In operation, it has been found that the structure of the bench in that type of cutter machine is subjected to large amounts of structural deformation. In particular, under the effect of the suction generated in the vicinity of the cutter conveyor, the guides along which the gantry moves can become so deformed as to be twisted. This leads to a corresponding deformation of the gantry involving friction and a loss of accuracy in the movements of the cutter head and to premature wear of those elements. Another drawback of those deformations is accelerated fatigue of the general structure of the cutter machine shortening its lifetime.
In an attempt to remedy those drawbacks, proposals have been made to stiffen the general structure of the cutter machine, e.g. by making the structure out of ever more rigid materials using ever increasing thicknesses, and adding structural reinforcement such as beams, stays, etc.
The consequence of applying those modifications is to considerably increase the weight and the cost of the cutter machine. Indirectly, costs involved with transporting and installing the machine are also increased because of the constraints put on preparing the premises where the machine is to be used.